The following is a tabulation of some prior art that presently appears relevant:
U.S. PatentsPat. No.Kind CodeIssue DatePatentee4,083,599Apr. 11, 1978Gaffney4,786,107Nov. 22, 1988Crockett4,946,222Aug. 07, 1990Matson4,993,777Feb. 19, 1991LaPointe5,061,010Oct. 29, 1991LaPointe5,165,753Nov. 24, 1992Henderson5,294,179Mar. 15, 1994Rudes, et. al.5,466,046Nov. 14, 1995Komorowski, et. al.5,984,411Nov. 16, 1999Galumbeck8,398,171B2Mar 19, 2011Lin and Tsai8,403,409B2Mar 26, 2013Pollard and Olcheski
A person who is infirm, either during recovery from a medical procedure, due to disease, or during old age, often has difficulty rising from a chair to a standing position upon a floor, a process known clinically as the “sit-to-stand task” or “sit-to-stand transfer”, and commonly known as “standing up” or “standing”.
Many prior-art devices address this problem, typically by raising the height of a chair's seat when a user of the chair wishes to stand. The effectiveness of raising a chair's seat to assist with sit-to-stand transfers is well known, as described at length in “Revolutionary advances in adaptive seating systems for the elderly and persons with disabilities that assist sit-to-stand transfers”, by Richard Edlich, Cynthia L. Heather, and Michael H. Galumbeck, appearing in the Journal of Long-Term Effects of Medical Implants, 2003, 13(1): 31:39, which is included herein in its entirety by reference, and also in “Determinants of the Sit-to-Stand Movement: A Review”, by Wim G M Janssen, Hans B J Bussmann, and Henk J. Stam, Journal of the American Physical Therapy Association and the Dutch Royal Society for Physical Therapy, 2002; 82:866-879, which is also included herein in its entirety by reference.
Prior-art devices for assisting with sit-to-stand transfer are separable into two categories; namely, a first category comprising specialty lift chairs that are built specifically for this purpose, and a second category comprising retrofittable devices that may be added to existing, ordinary chairs. Prior-art examples in the first category include U.S. Pat. No. 4,946,222 (Matson, 1990), U.S. Pat. No. 5,061,010 (LaPointe, 1991), U.S. Pat. No. 5,165,753 (Henderson, 1992), U.S. Pat. No. 5,466,046 (Komorowski, 1995), U.S. Pat. No. 5,984,411 (Galumbeck, 1999), U.S. Pat. No. 8,398,171 B2 (Lin and Tsai, 2011), and U.S. Pat. No. 8,403,409 B2 (Pollard and Olcheski, 2013). Prior-art examples in the second category include U.S. Pat. No. 4,786,107 (Crockett, 1988), U.S. Pat. No. 4,993,777 (LaPointe, 1991), and U.S. Pat. No. 5,294,179 (Rudes et al., 1994).
A third category of devices comprises retrofits to existing lift chairs that provide functions other than lifting. An example of this category is U.S. Pat. No. 4,083,599 (Gaffney, 1978), which provides rocking and wheeling functions for an existing lift chair. Devices in the third category are not germane to the current discussion because they themselves do not provide the chair-lifting function.
Devices in the first category—specialty lift chairs—are sold, for example, by La-Z-Boy® Incorporated of Monroe, Mich.; Pride Mobility Products of Exeter, Pa.; Golden Technologies of Old Forge, Pa.; AmeriGlide Inc. of Raleigh, N.C.; Easy Comforts of Oshkosh, Wis.; and others. Unfortunately, some infirm and older people who replace a favorite, comfortable, ordinary chair, such as a recliner, with one of the rising-and-tilting models are disappointed because of reduced comfort. Comfort in seating is highly individual; infirmity should not force a person to replace a favorite chair with a less-comfortable lifter chair, particularly if sit-to-stand assistance is needed only for a limited time, such as following a knee-replacement operation, as described in Edlich et al. previously cited, or following a posterior hip-replacement operation to avoid excessive hip flexion, as described in “Flexion reminder device to discourage recurrent posterior dislocation of a total hip replacement: a case report”, by King Wong et al., Journal of Medical Case Reports, 2008, 2:250. Consequently, there is a need for a device that may be retrofitted to a normal chair—any chair of the user's choice—to provide sit-to-stand assistance.
Such is the motivation for devices in the second category—retrofittable devices that may be added to an existing, ordinary chair that normally rests upon a floor. Such an ordinary chair typically has a seat that is a fixed height above the floor. A typical, prior-art retrofit allows a user of the ordinary chair, when the user wishes to stand up, to increase the seat height from a low position used for sitting to a high position. This helps the user to stand. Conversely, the retrofit allows the user, when wishing to sit down, to decrease the seat height from the high position to the low position. This helps the user to sit.
Definitions
LetH≡A vertical distance from the floor to a seat surface of the chair, also called “the seat”, measured at the front of the seat.  (1)R≡For a chair-lifting retrofit, a vertical distance from the floor to a base plane defined by a base of the chair, measured on a line defined by the intersection of the base plane with a vertical plane through the front of the seat.   (2)H0≡The value of H for a chair without a retrofit.  (3)HSIT≡The value of H for a chair with the retrofit in its low position.  (4)HSTAND≡The value of H for a chair with the retrofit in its high position.  (5)RSIT≡The value of R when the retrofit is in its low position; that is, the low-position “overhead” of the retrofit.  (6)RSTAND≡The value of R when the retrofit is in its high position.  (7)ΔR≡RSTAND−RSIT≡Amount by which the retrofit raises the base plane of the chair, measured at the front of the seat, as the retrofit moves from the low position to the high position.  (8)ΔH≡HSTAND−HSIT≡Amount by which the retrofit raises the seat of the chair, measured at the front of the seat, as the retrofit movies from the low position to the high position.  (9)
From these definitions, it follows thatHSIT=H0+RSIT,  (10)HSTAND=H0+RSTAND,  (11)ΔH=ΔR.  (12)
Note that definitions (3) through (12) above are deliberately stated in terms of the height of the chair at the front of the seat, because this is what matters most in helping the user to stand. Standing may be accomplished only when the user's center of gravity moves forward of the heels of his or her feet, as described in Edlich et. al. cited earlier. Consequently, if the user's buttocks remain toward the rear of the seat, far behind the heels, standing is more difficult, because the body's center of mass is too far back, requiring a greater forward-leaning angle of the torso. Rather, the user should move his or her body's center of mass forward as much as possible, before attempting to stand, by sliding the buttocks forward toward the front of the seat. This also insures that the user's feet will remain in contact with the floor as the seat rises, as required for safety. Such a strategy is often recommended for people with bad backs and for pregnant women (e.g. http://my.clevelandclinic.org/healthy_living/back_health/hic_posture_for_a_healthy_back.aspx); in general, it is a task that many infirm people are able to accomplish easily and without assistance in typical chairs. Once the buttocks are repositioned toward the front of the chair, the height of the rear portion of the seat doesn't matter because the user is no longer in contact with the rear of the seat. Moreover, once the buttocks are repositioned toward the front, the forward tilt of the seat (provided by many specialty lifter chairs as well as prior-art retrofits) doesn't substantially matter either, for the same reason. Only the height of the front portion of the seat matters.
First Desirable Attribute
Consequently, a first desirable attribute of a chair-lifting retrofit is that the amount of seat rise provided, measured at the front of the seat, be large. That is, ΔR (=ΔH) should be large. If not-so-demanding users requires less change in seat height than the amount ΔH provided by the retrofit, they are free to use less, because a retrofit chair lifter typically can move to any position within its range and stop on demand. To determine how large ΔH should be for the most demanding users, consider results reported by Edlich et al., previously cited: for normal chairs, average seat heights vary fromH0=381 mm=15″ for living rooms  (13)toH0=422 mm=16.6″ for nursing homes,  (14)whereas sit-to-stand performance is aided by lifting the seat height to as much asHSTAND=610 mm=24″.   (15)
An adequate value for ΔH may be computed fromΔH=ΔR=HSTAND−HSIT=HSTAND−(H0+RSIT),  (16)where the latter equality uses equation (10). Thus, for an ideal retrofit in which the low-position “overhead” RSIT is zero (see “Second Desirable Attribute”, below),ΔH=HSTAND−H0 (for ideal case RSIT=0),  (17)whence, using the values in equations (15) and (13), an adequate amount of seat rise isΔH=ΔR=(610−381)mm=229mm=9.0″.   (18)
Consequently, prior-art retrofits that fail to raise the front portion of the seat at least this much are deficient.
Second Desirable Attribute
A second desirable attribute of a chair-lifting retrofit is that the low-position “overhead” imposed by the retrofit, RSIT, defined by equation (6), be as close to zero as possible, because the user, sitting for extended periods of time with the retrofit in the low position, is likely to be very uncomfortable when RSIT is considerably larger than zero, inasmuch as his or her feet may be unsupported, or only partially supported, on the floor, particularly if his or her lower legs are short.
Consider how large a value of RSIT is acceptable. Although seat heights vary considerably from person to person, the presumption in designing a chair-lifting retrofit must be that the user's own chair is comfortable for the user; that is, the seat height H0 is comfortable. Thus, when in the low position, the retrofit should alter H0 as little as possible, because the user's comfort is indeed quite sensitive to the value of the HSIT.
As stated by ergonomics experts (http://ergo.human.cornell.edu/dea3250notes/sitting.html): “Minimum height [of a seat] should be 15” (38 cm) . . . Fixed height should be 17″ (43 cm). This is a compromise. A chair that is too high leads to increased pressure at the popliteal fold (underside of knees), decreasing blood circulation and increasing pressure on the nerve. A chair that is too low increases weight on the ischial tuberosities [the sitting bones]”. Note how closely the values stated in this passage agree with equations (13) and (14). It is concluded that variation beyond the 50-mm (2-inch) range sited by these sources is unacceptable. Thus, a chair-lifting retrofit must be limited to at mostRSIT≦50 mm (2″),  (19)and the closer RSIT is to zero, the better.Third Desirable Attribute
A third desirable attribute of a chair-lifting retrofit is that, at the front of the chair where the feet are placed, there should be no obstructions at or near floor level when the retrofit is in the high position, so that the user's feet may be placed rearward of the front of the seat prior to standing. Define an available foot space F asF=Horizontal distance, projected onto the plane of the floor, measuring rearward from the projected front edge of the chair's seat to the nearest element of the retrofit that, in its high position, abuts or is near the floor in a manner that may prevent the user from moving his or her feet rearward.  (20)
For a chair-lifting retrofit, F is important because moving the feet rearward at the onset of standing, known as “posterior foot placement”, minimizes the forward rotation of the torso required to position the body's center of gravity forward of the heels. That is, allowing posterior foot placement (i.e. larger F) helps the user to stand. This is discussed in Edlich et al. (previously cited), citing a study by Kawagoe (Kawagoe, S., Tajimi N, Chosa E., “Biomechanical analysis of foot placement with varying chair height on the motion of standing up”, J. Orthop Sci 2000; 5:124-133). Edlich concludes: “in addition to being of adequate height, chairs should have enough space beneath the seat to permit posterior foot placement.” Thus, F should be large enough to allow any user as much room as desired to move the feet rearward.
To estimate an adequate value for F, letθKNEE≡Backwardly inclined angle of lower leg with respect to vertical,  (21)and assume that, in the high position of the retrofit, the back of the user's legs, backwardly inclined at angle θKNEE, are, to aid standing as much as possible, snuggly against the front edge of the retrofit's supporting platform located distance RSTAND from the floor. Assuming the platform to be relatively thin, the user's heels are therefore rearward of the front of the platform by an amountF=RSTAND tan θKNEE.  (22)
Literature (e.g. Camargos et. Al., “The Effects of Foot Position on the Performance of Sit-to-Stand Movement with Chronic Stroke Subjects”, Arch. Phys. Med. Rehabil, Vol. 90, February 2009) suggests that a typical backwardly inclined knee angle during the sit-to-stand movement isθKNEE=15°.  (23)
Assuming equation (18) with the ideal case RSIT=0 yields RSTAND=229 mm, whence the value of F required to avoid interference with the posterior foot placement is estimated, using equations (22) and (23), to beF=(229 mm)tan 15°=61 mm.  (24)
Consequently, it is desirable that a chair-lifting retrofit provide at least this much clear space at floor level rearward of the front of the chair seat.
Fourth, Fifth, and Sixth Desirable Attributes
A fourth desirable attribute of a chair-lifting retrofit is that it be universally applicable to all types of chairs without custom engineering, and without modifying the chair.
A fifth desirable attribute of a chair-lifting retrofit is that its mechanism should avoid occupying space between the base of the chair and the underside of its seat. A retrofit lacking this attribute lacks general usefulness, because for many chairs, including most popular recliner models, no such space is available—the mechanism of the chair itself already occupies virtually all the space between its base and its seat.
A sixth desirable attribute of a chair-lifting retrofit is that it should be easily deployed and easily un-deployed. This is important, for example, if the retrofit is used with a given chair only for a short time, on a rental basis for example, implying that the retrofit must be redeployed repeatedly with different chairs. Consequently, as for the fourth desirable attribute, deployment should not involve modifying the chair, such as penetrating its members with fasteners. Moreover, the retrofit should disassemble into a small number of pieces, each of which is compact and easily manageable.
Shortcomings of Prior Art
Every prior-art chair-lifting retrofit suffers from one or more of the following shortcomings:
(a) It fails to have the first desirable attribute; that is, ΔR is too small. Thus the prior-art retrofit fails to provide sufficient sit-to-stand assistance, the very task it purports to accomplish.
(b) It fails to have the second desirable attribute; that is, RSIT is too large. Thus the prior-art retrofit makes sitting uncomfortable.
(c) It fails to have the third desirable attribute; that is, F is too small. Thus the prior-art retrofit is less effective at helping the user stand because it does not allow sufficient posterior foot placement.
(d) It fails to have the fourth desirable attribute; that is, it requires custom adaptation to be effectively and safely used with different types of chairs. For example, some prior-art retrofits, as will be shown, cause the chair to tilt forward. To avoid danger in such cases, the chair must be well secured to the retrofit. Yet each chair is different, so a custom scheme must be developed to secure it to the retrofit. Consequently, prior-art retrofits that tilt forward lack general usefulness, because they cannot be adapted to a wide variety of chairs without costly and time-consuming custom engineering. Moreover, in most cases, the chair must be modified to achieve safe retrofit-to-chair attachment; for example, the chair's frame members must be penetrated by fasteners such as screws, which is undesirable.(e) It fails to have the fifth desirable attribute; that is, its mechanism fails to avoid occupying some of the space between the base of the chair and the underside of the seat. Such a retrofit lacks general usefulness, because for many chairs, including most popular recliner models, no such space is available—the mechanism of the chair itself already occupies virtually all the space between floor and seat. Typically, prior-art retrofits suffer from shortcoming (e) because they attempt thereby to avoid shortcoming (b).(f) It fails to have the sixth desirable attribute; that is, it cannot be easily deployed and un-deployed, for one or more reasons. It may require modification of the chair, or otherwise involve difficult and time-consuming assembly. It may be monolithic and therefore be too cumbersome and heavy to move easily. Conversely, it may disassemble into too many pieces, and therefore be difficult to manage.
With regard to these six shortcomings (a) through (f), consider specifically each piece of previously cited prior art in the second category (i.e. retrofits), including U.S. Pat. No. 4,786,107 (Crockett, 1988), U.S. Pat. No. 4,993,777 (LaPointe, 1991), and U.S. Pat. No. 5,294,179 (Rudes et al., 1994). To summarize, Crockett's retrofit suffers from shortcomings (a), (b), (c), (d) and (f); LaPointe's retrofit suffers from shortcomings (a), (e), (f) and to some extent from (b) and (c); and Rudes's retrofit suffers from shortcoming (a), (b), (d), and (f), and may suffer from (c).
Specific Prior Art: Crockett (U.S. Pat. No. 4,786,107) (FIGS. 1 through 3)
Crockett's chair-lifting retrofit suffers from shortcoming (b): RSIT is too large. Consider Crockett's FIGS. 1, 4 and 5, duplicated here with annotations as FIGS. 1, 2, and 3, respectively. FIGS. 2 and 3 illustrate side views of Crockett's retrofit: FIG. 2 shows the retrofit in a high position; FIG. 3 shows it in a low position. In the low position, the mechanism adds seat-height overhead RSIT to the normal seat-height of the chair seat. Crockett does not state a value for RSIT, but it must be large enough to accommodate a certain minimum angle of the riser arm (Crockett's reference numeral 64), this angle being denoted θ on FIG. 3; otherwise, the force required from Crockett's power means (reference numeral 44 of Crockett's FIG. 2, not shown here), would become so large that no practical power means could deliver it, inasmuch as the required force varies as the cotangent of angle θ, which rises to infinity as θ approaches zero. Moreover, Crockett's value of RSIT must be large enough to accommodate the power means itself. For both these reasons, Crockett's value of RSIT is estimated to be 75 mm or more, which violates the requirement (19), which states that RSIT should be limited to 50 mm, and preferably be smaller. Consequently, Crockett's retrofit fails to provide comfortable sitting for the user.
Crockett's retrofit further suffers from shortcoming (a); that is, ΔR is too small. Crockett does not state a typical value of ΔR achieved by his apparatus, but scaling in FIGS. 2 and 3 shows
                                          Δ            ⁢                                                  ⁢            R                                R            SIT                          =                                                            R                STAND                            -                              R                SIT                                                    R              SIT                                =                      1.59            ⁢                                                  ⁢                                          (                Crockett                )                            .                                                          (        25        )            
Assuming the value RSIT=75 mm estimated in the previous paragraph impliesΔR=119 mm=11.9 cm=4.7″(Crockett).  (26)
This value of ΔR is far less than the desired value of 229 mm (9.0″) stated in equation (18). Consequently, Crockett's retrofit provides insufficient sit-to-stand assistance for many users.
Crockett's retrofit further suffers from shortcoming (c), because front base member 26, which remains at floor level even when the retrofit is in the high position (FIG. 2), traverses the entire width of the apparatus, as shown in FIG. 1. Consequently, it forms an obstruction that may prevent the user from the desired posterior foot placement. Crockett does not state a value of F, and the position of the front of the chair seat is with respect to Crockett's front base member 26 is unclear. However, assuming the front of the chair seat aligns with the front bracket 48, as shown by the dashed line 202, scaling in FIG. 2 shows
                              F                      R            SIT                          =                  0.54          ⁢                                          ⁢                                    (              Crockett              )                        .                                              (        27        )            
Using the value RSIT=75 mm assumed above impliesF=40 mm (Crockett).  (28)
This is somewhat less than the value of 61 mm stated in requirement (24), so Crockett's retrofit may well interfere with posterior foot placement. The result depends on the assumed position of dashed line 202. Nevertheless, a lifter assembly without a front base member such as Crockett's 26 would be superior, because it would rule out any possibility of interference with posterior foot placement.
Crockett's retrofit also suffers from shortcoming (d). As stated in Crockett's column 2, lines 54-57: “The attachment means . . . may be replaced with clips, straps, bands, bolts, screws, etc. to accommodate a particular seating structure's . . . or user's requirements.” That is, deploying the retrofit safely requires a varied array of attachment solutions that must be separately engineered for various types of chairs, and likely involves altering the chair by penetration of fasteners and the like. The general usefulness of Crockett's retrofit is thereby compromised.
Finally, Crockett's retrofit suffers from shortcoming (f), not only because it may require modification of the chair, as already mentioned, but also because it is a monolithic structure which is likely to be too heavy and cumbersome to be easily moved and stored.
Specific Prior Art: La Pointe (U.S. Pat. No. 4,993,777) (FIGS. 4 through 7)
LaPointe's chair-lifting retrofit suffers from shortcoming (a). Consider LaPointe's FIGS. 1 and 2, which are reproduced here as FIGS. 4 and 5 respectively. Referring to these figures, La Pointe states the following at column 2, lines 55-58: “the height 21 of the seat 11 above the floor is about 17 inches in the seated position of [FIG. 5] and about 18 inches in the fully elevated position of [FIG. 4].” That is, the important portion of the seat—the front—is raised only byΔR=1″=25 mm (LaPointe).  (29)
This is far less than the required value of 229 mm stated in equation (18). To be sure, because of the forward tilt angle that LaPointe provides (29°), the rear of the seat is raised much more, but this is largely ineffective in helping the user to stand, because to be in contact with the rear portion of the seat, the user's center of gravity must be so far back that it cannot possibly be forward of the heels, which is required to achieve the sit-to-stand task. Thus, LaPointe's retrofit provides far too little seat rise to help appreciably with the sit-to-stand process.
LaPointe's retrofit is on the borderline of suffering from shortcoming (c). Consider LaPointe's FIG. 4, reproduced here as FIG. 6. Referring to this figure, La Pointe's base assembly 1 comprises a wooden front cross member 39 that extends across the front of the mechanism. Because the cross member rests nearly at floor level almost directly beneath the front edge of the seat 11, it may well violate requirement (24) that quantifies the requirement to avoid interference with posterior foot placement. LaPointe does not state a value of the foot clearance F, but it may be estimated by from FIG. 4, where by measurement
                              F                      H            BACK                          =                  0.0427          .                                    (        30        )            
At column 2, lines 62-63, LaPointe says that dimension HBACK=55.5″, whence, from (30),F=2.37″=60 mm,  (31)which is only slightly in violation of requirement (24). At best, LaPointe's allowance for posterior foot placement is only minimally acceptable. Nevertheless, a lifter assembly without a front cross member such as LaPointe's 39 would be superior, because it would rule out any possibility of interference with posterior foot placement.
LaPointe's retrofit further suffers from shortcoming (e), and to some extent from (b), as stated in column 3, lines 15-19: “The mechanism to be described nests inside of the wooden frame member and the bottom of the chair 3 and . . . the assembly 1 is of low profile and increases the seat height by only about 2 inches.” That is, LaPointe tries to minimize shortcoming (b), achieving RSIT=2 inches (and thus barely satisfying requirement (19)), but he does so by introducing shortcoming (e), assuming unrealistically, as shown in his FIG. 6 (FIG. 7 herein), that his mechanism can protrude into space beneath the chair's seat. Although this assumption was apparently valid for the particular type of chair he was considering, as described (per LaPointe) in U.S. Pat. No. 4,367,895, it is not valid for most chairs, particularly popular modern recliners, whose internal mechanisms already fill this space. Consequently, LaPointe's retrofit can only be used with a very limited subset of chairs.
Finally, LaPointe's retrofit suffers from shortcoming (f), not only because it requires modification of the chair, as already mentioned, but also because it is a monolithic structure which is likely to be too heavy and cumbersome to be easily moved and stored.
Specific Prior Art: Rudes et al. (U.S. Pat. No. 5,294,179) (FIGS. 8 through 10)
Rudes's chair-lifting retrofit suffers from shortcoming (a). Consider Rudes's FIGS. 1, 5, and 3, which are reproduced here as FIGS. 8, 9, and 10 respectively, annotated to show RSIT on FIG. 9 and RSTAND on FIG. 10. Scaling shows that
                                                        R              STAND                                      R              SIT                                =                      2.73            ⁢                                                  ⁢                          (              Rudes              )                                      ,                            (        32        )            whence
                              Δ          ⁢                                          ⁢          R                =                                            R              SIT                        ⁡                          (                                                                    R                    STAND                                    -                                      R                    SIT                                                                    R                  SIT                                            )                                =                                                    R                SIT                            ⁡                              (                                                                            R                      STAND                                                              R                      SIT                                                        -                  1                                )                                      =                          1.73              ⁢                                                          ⁢                              R                SIT                            ⁢                                                          ⁢                                                (                  Rudes                  )                                .                                                                        (        33        )            
At column 2, lines 27-37, Rudes states that “the present invention . . . [has] the advantage of an unusually compact lifting and tilting device with a retracted height of only about 4.5 inches.” In other words,RSIT=4.5″=114 mm (Rudes).  (34)
Substituting equation (34) into equation (33),ΔR=197 mm=7.8″ (Rudes).  (35)
This violates the requirement (18). Consequently, Rudes's retrofit provides insufficient sit-to-stand assistance for certain users.
Rudes's chair-lifting retrofit further suffers from shortcoming (b) as revealed by the same passage just cited, at column 2, lines 27-37, which is expressed as equation (34). Although Rudes describes his seat-height overhead of 4.5 inches as “unusually compact”, this overhead is actually very large, being seriously in violation of requirement (19). Consequently, Rudes retrofit will produce great discomfort while the user is sitting.
Regarding shortcoming (c), Rudes does not show clearly the fore-to-aft placement of the chair upon the retrofit. Consequently, it is hard to access whether Rudes's retrofit suffers from shortcoming (c); that is, whether it violates requirement (24) and thus interferes with posterior foot placement by the user. FIGS. 8-10 certainly suggests that it will violate requirement (24), inasmuch as the frontal support bar 36 (identified in FIG. 10) extends at floor level across the entire width of the retrofit, and this frontal support bar lies forward of the frontal portion 24 of the platform. In FIG. 10, reference numeral 19 is “the bottommost part of the chair frame”, but it is unclear from this drawing where the front of the chair's seat is located vis-à-vis the frontal portion 24 of the platform. In any case, a lifting apparatus without such a floor-level frontal bar 36 would be superior, because it would rule out any interference with posterior foot placement.
Rudes's retrofit further suffers from shortcoming (d), in that it causes the chair to tilt forward, and, as previously mentioned, a retrofit providing forward tilting requires, for safety reasons, means to secure the chair to the retrofit. This makes it highly unlikely that such a retrofit can be universally adapted to a wide variety of chairs. Indeed, although Rudes contends, in column 1, lines 45-46, that his retrofit is “universal adaptable to most previously manufactured chairs”, the scheme he actually describes is hardly universally adaptable. That is, at column 4, lines 4-8, he states that “The peripheral edge of the bottommost part of chair frame 19 [FIG. 10 herein], shown in partial view by broken lines, is bolted to platform 16 through multiple mounting flanges 20 having expanded openings 22 for threaded connectors”. This is not adaptable, for example, to chairs with four legs rather than a base frame. Nor is it adaptable to rocker-style recliners with round bases. Even upholstered chairs with rectangular base frames—the type of chair Rudes attempts to accommodate—are unlikely to have frame members that line up with the “expanded openings” of a particular platform design; to accommodate the large number of base-frame sizes in the marketplace, many platform variations would have to be manufactured. Thus, much custom engineering and expense is required to adapt Rudes retrofit to a wide variety of chairs, thereby compromising its general usefulness. Moreover, even if a chair happens to accommodate Rudes attachment scheme, alteration of the chair itself is still required, in the form of the “threaded connectors” that must be driven into the wooden frame of the chair. This is undesirable; it is preferable not to alter the chair at all.
Finally, Rudes's retrofit suffers from shortcoming (f), not only because it requires modification of the chair, as just mentioned, but also because it is a monolithic structure that is likely to be too heavy and cumbersome to be easily moved and stored.